In the related art, a superconducting accelerator which accelerates charged particles such as electrons or protons by using a superconducting acceleration cavity is known.
Such a superconducting accelerator is disclosed in, for example, PTL 1. In the superconducting accelerator, a superconducting acceleration cavity formed of a superconducting material is cooled by a refrigerant such as liquid helium and made to be superconductive, whereby electric resistance becomes almost zero, so that the acceleration of charged particles is efficiently performed with small electric power.
Incidentally, in the superconducting accelerator, a magnetic shield for shielding against geomagnetism which adversely affects the superconducting characteristics in the superconducting acceleration cavity, and a radiation shield for suppressing the incidence of radiant heat from the outside on the superconducting acceleration cavity are provided so as to cover the superconducting acceleration cavity.
The magnetic shield is usually configured of a magnetic body and performs shielding by bypassing and absorbing the magnetism in a shield space. The radiation shield is cooled with a refrigerant (liquid helium, liquid nitrogen, or the like) and absorbs the radiant heat just before the superconducting accelerator.